This invention relates to antennas and more particularly to a vertically polarized omnidirectional antenna.
In various antenna requirements, there is need for an omnidirectional antenna of relatively high gain. Specifically, in the field of vehicular communication, there is needed a vertically polarized omnidirectional antenna of relatively high gain. One method of providing this requirement is to utilize a vertical array of colinear dipoles. Typically, colinear cylindrical dipoles are employed which are centrally fed by a coaxial transmission line. Such a vertical array provides the necessary vertical polarization and produces an omnidirectional pattern in the horizontal plane.
Another prior art solution to providing this requirement is to utilize vertical dipoles which are mounted a considerable distance from a vertical support member which member contains the transmission lines which feed the dipoles. Typically, at least several wavelengths distance are required between the dipoles and the vertical support to provide omnidirectional coverage, or alternatively several dipoles are required at each level.
Each of the prior art proposed solutions have limitation. For example, utilizing a vertical array of colinear dipoles is quite complex and operates well over only a narrow frequency band. Also, it is limited in power handling, in maximum obtainable gain, and in obtaining beam downtilt and null fill-in in the vertical plane. On the other hand, utilizing vertical dipoles which are side mounted require large size and also may depart from the designed omnidirectional horizontal coverage.